There is no single specific diagnostic tool used to diagnose sarcoidosis.  It can be difficult to diagnose as the symptoms and laboratory results can occur in other diseases, and may mimic other disorders.  The primary tools used to diagnose sarcoidosis may include:

Medical history and physical exam to look for signs of sarcoidosis and to eliminate the possibility of other diseases. 

Chest X-rays to look for enlarged lymph nodes, small round spots, or cloudiness in the lungs.

Pulmonary function tests to assess how well the lungs are working.

Bronchoscopy to inspect the bronchial tubes and to take a tissue biopsy to look for granulomas, and to rule out infection.  During a bronchoscopy, a small tube is passed down the windpipe and into the airways of the lungs.

An eye exam to look at the inside of the eye for any signs of sarcoidosis.  

Blood tests to measure any unusual changes in the liver and kidney function.

A CT scan to identify any enlarged lymph nodes or scarring in the lungs that may not appear in a regular chest X-ray.

A Gallium scan to verify the presence of sarcoidosis in many organs.

Positron emission tomography (PET) scan or magnetic resonance imaging (MRI) to determine if the heart or central nervous system have been affected by sarcoidosis.

An electrocardiogram (EKG) to record the electrical activity of the heart, shows how regularly the heart beats, and determine if there is any strain on the heart.

Biopsies of a small sample of tissue may be taken from a part of the body to look for granulomas if it is believed to be affected by sarcoidosis.